Prof. B. Silliman on some American Minerals. 459 



99-36 



I have never seen the Worthite, and have therefore no 

 means of judging of the similarity of these two minerals in 

 other respects. The probability of being able to refer the 

 present mineral to kyaiiite seemed to me at first quite strong, 

 but I was unable by any care to procure an amount of silica 

 less than that given in these analyses Should this mineral 

 on further examination and comparison prove to be distinct, 

 I propose for it the name Monrolite, derived from the locality 

 where it was found. 



IV. On the identity of Sillimanite, Fibbolite and 



BUCHOLZITE WITH KyaNITE. 



Sillimanite was orginally described by Bowen*, from an 

 analysis made in Yale College Laboratoy in 1825, which 

 showed it to be a silicate of alumina with a proportion of silica 

 too high to allow it to come within the formula of kyanite. It 

 was subsequently analysed by Dr. Thomas Muir, in the labo- 

 ratory of Dr. Thomson, who found in it a large quantity of 

 zirconia, an observation which all subsequent researches have 

 failed to confirm. Since that time it has been analysed by 

 various chemists ; viz. by Connel, Norton, Staff, Hayes and 

 Thomson. The most recent of these analyses which has been 

 published is that by Thomson, who reports it to contain 45*65 

 per cent, of silica. We have then the following discordant 

 results in the amount of silica found in Sillimanite by different 

 chemists in the order of their publication : — 



1. 2. 3. 4. 5. 6. 7. 



Bowen. Muir. Connel. Norton. Staff, Hayes. Thomson. 



Percent. 42-67 38-67 3675 37*40 37*36 42*60 46*65 



The cause of this disagreement will undoubtedly be found 

 in the difficulty of effecting a complete decomposition of an- 

 hydrous silicates of alumina, which contain a high per-centage 

 of alumina. This decomposition can be completely effected 

 only by the aid of caustic potash applied to the mixture of 

 carbonates and the mineral during the fusion, as first recom- 

 mended by Berzelius, or by hydrofluoric acid. 



Select crystals of this mineral were taken from the original 

 locality at Chester, Conn., and their analysis afforded the 

 following results. Quantity taken, 775*5 grms. Found — 



* Journ. Acad. Nat. Sci.Phil., iii. p. 375. 



